This invention relates to a system for connecting a roadside structure, such as a highway sign, to a support surface, and in particular to a system that allows the structure to be broken away upon being impacted by an errant vehicle.
Roadways and highways have numerous necessary structures located along their sides. For instance, almost every single highway has highway sign posts, commercial sign posts, luminaire supports, emergency call box supports, and fire hydrants located therealong. It is necessary for these structures to be located in close proximity to the road. These structures present significant hazards to an errant vehicle that exits the roadway and impacts the structures. If the structures are rigidly fixed adjacent the roadside, contact by a vehicle with the structure will result in significant damage to the vehicle and potentially serious bodily harm to the vehicle occupants. In fact, if such structures are rigidly secured, the chance of a fatality occurring in a collision dramatically increases. More specifically, a moving vehicle contacting a fixed, rigid support is subject to significant deceleration and generates an incredible amount of force that results in a very violent collision. A roadside structure that will breakaway or yield upon impact by a vehicle will greatly reduce the severity of the collision and is less likely to result in bodily harm to the vehicle occupants.
Numerous attempts have been made in the past to provide connections between roadside structures and a ground support surface. Once of the most basic types of prior art structures involves the use of yielding supports. More specifically, a structure, such as a sign, is supported by a yielding rod-like structure. When a vehicle impacts the rod-like structure, the rod simply bends over and out of the way of the impacting vehicle. These types of yielding support structures are typically only suitable for small highway structures. More particularly, in order to support large highway structures, a support rod or the like must have a particular rigidity to hold the structure in the upright position, especially when the structure is subjected to wind loading. Oftentimes, the rigidity of the material utilized to support the large structure is such that if contacted by a vehicle, a significant amount of force is still generated, thus resulting in a violent collision. Additionally, as is apparent, in order to adopt existing roadside structures to utilize yieldable supports, it is necessary to re-anchor the support in the ground utilizing the yielding support structure.
A further type of highway structure connection is a slip-base connection. In this type of connection, an anchor member extends from the ground and has a rigid plate secured thereto. The support member used to support the structure also has end plate that rests on the anchor member end plate. Notches are provided on the edges of the end plates of the adjoining anchor member and support member. Bolts are placed in these edge notches to connect the two end plates together and, thus, to connect the support member to the anchor member. The edge notches are such that they allow the bolts to slip out of the connection when the structure is contacted by a vehicle. A keeper plate is commonly used to hold the bolts and prevent the bolts from slipping out of the edge notches due to wind induced vibration and temperature-induced expansion and contraction. These types of structures suffer from the disadvantage that they are oftentimes not omnidirectional. More specifically, if a vehicle contacts the supported structure in a force line that is not in line with the edge notches, a substantial amount of force can still be generated by a collision. Further, it is typically difficult to adopt existing roadside structures to the slip base devices. Additionally, the clamping force must be between specific ranges to allow the bolts to slip, but still resist wind loads and temperature variations. Therefore, during installation, the torquing of the bolts to obtain the correct clamping force is crucial, thus requiring substantial time and attention to detail during preparation.
A still further type of roadside connector is a frangible transformer base. A frangible transformer base consists of a pedestal that is manufactured from a brittle material, typically aluminum. The frangible base is used to support the highway structure and attaches the support member to a rigid base, such as a concrete foundation. When a vehicle impacts the highway structure, the frangible transformer base fractures, allowing the supporting member to breakaway from the rigid base and move out of the way of the errant vehicle. As is apparent, it is oftentimes difficult to modify existing structures to use frangible transformer bases. Still further, frangible transformer bases are typically expensive to manufacture and can require numerous different sizes be made for different sizes of structure.
A still further type of roadside connector is frangible couplers. These couplers are often placed between a plate attached to an anchor member and a plate attached to a support member. When the highway support structure is impacted, the frangible couplers fracture and allow the support and anchor members to separate, thus reducing the potential for injury to the vehicle occupants. The first type of frangible coupler consists of a generally cylindrically fabricated body formed of a brittle matrix material. On one end of the cylinder a short threaded rod is cast into the brittle matrix material and presents male threads for connection to the attachment plate of a support member. The other end of the cylinder has a threaded sleeve formed therein that presents a female thread surface that is capable of mating with a male-threaded stud of an anchor member. A second type of frangible coupler consists of a solid shaft that is machined with threads on each end and with an hourglass configuration in the middle region between the threaded ends. The hourglass-shaped middle region presents a reduced cross section for fracturing upon contact. Frangible couplers are typically expensive and difficult to manufacture because they require the machining of special features, such as an hourglass configuration, that result in high labor and machine costs. Additionally, because of the difficulty of manufacturing frangible connectors, it is oftentimes difficult to adopt existing highway structures for their use. More specifically, an existing highway structure has a particular weight and height that results in certain wind load and gravitational forces being applied to the base of the support structure. Therefore, existing off-the-shelf frangible couplers oftentimes lack a sufficient number of sizes and types to retrofit a great number of existing supports. In particular, the sizes available may not provide sufficient resistance to wind loading while allowing sufficient breakaway capacity to reduce injury due to collision. If this is the case, it may be necessary to custom manufacture the frangible coupler which results in very high manufacturing costs due to the potential intricate molding and milling processes required to make these couplers.
Therefore, a breakaway connection system is needed which will overcome the problems with the prior connecting structures discussed above.